1. Field of the Invention
The present invention relates to improved copolyester plasticizer compositions useful for the formulation of PVC refrigerator gaskets which exhibit good resistance to migration and marring and improved processing characteristics.
2. Description of the Prior Art
For a compound is to be an effective plasticizer for PVC and impart the desired softening, flexibilizing and toughening, the material must have some mobility within the PVC resin. If this mobility is not properly controlled, however, the plasticizer can migrate into other resins with which the plasticized PVC comes in contact.
Migration of PVC plasticizers into high impact polystyrene and acrylonitrile-butadiene-styrene (ABS) resins is a particular problem. Many of the ester compounds commonly used for the plasticization of PVC mar the surface of the polystyrene or ABS in those regions where the resins come into contact with the plasticized PVC. In severe cases, stress cracking of the polystyrene and ABS resulting in rapid and catastrophic failure of the resin can occur.
Various polyester compositions have been developed to overcome the above-described problems. These polyesters are typically derived from branched-chain diols and aliphatic dicarboxylic acids. Viscosities are controlled by the use of conventional monocarboxylic acid or monofunctional alcohol terminators. Whereas acceptable migration characteristics can be achieved with these polyesters, the plasticizers are more expensive than polyesters based on phthalates and ethylene glycol. Copolyesters containing phthalates and copolyesters wherein all or a portion of the propylene glycol is replaced with ethylene glycol have heretofore been found to have unacceptable mar characteristics.
Williams et al., U.S. Pat. No. 3,972,962 discloses chain-terminated non-migrating polyester plasticizers for PVC derived from aliphatic saturated dicarboxylic acids and branched-chain glycols. An aromatic monocarboxylic acid is necessarily employed as a chain terminator to obtain the desired balance of plasticizer properties.
Aylesworth et al. in U.S. Pat. Nos. 3,501,554 and 3,595,824 disclose non-chain terminated polyester plasticizers for PVC fabrics obtained by the reaction of two or more alkanedioic acids having from 4 to 12 carbon atoms with two or more alkylene glycols having from 2 to 6 carbon atoms. The Aylesworth et al. plasticizer compositions exhibit superior resistance to drycleaning solvents, such as perchloroethylene.
Lamont et al. U.S. Pat. No. 4,122,057 discloses polyesters which are terminated with a mixture of an aliphatic monobasic acid and a monofunctional alcohol. As a result of this mixed-termination, plasticizers having improved low temperature properties are obtained.
Copolyester plasticizers and a process for their production are also described in Uno et al., U.S. Pat. No. 4,065,439. The copolyesters of Uno et al. are derived from terephthalic acid, isophthalic acid, a C.sub.6-9 aliphatic dicarboxylic acid, ethylene glycol, and neopentyl glycol. These copolyesters are solid materials primarily useful as hot-melt type adhesives, however, they may also be used for paints, surface treating agents, binders and plasticizers.
U.S. Pat. No. 3,700,957 to Daniels discloses polyester compositions having both flame retarding and plasticizing properties obtained by the reaction of a dicarboxylic acid, a glycol and 2,3-dibromomethyl-1,3-propanediol. The polyesters may be terminated with an alkanoic acid or alkanol chain terminator.
Other polyester plasticizers derived from diols and dicarboxylic acids are disclosed in Small et al., U.S. Pat. Nos. 2,555,062; Wilkinson et al., 2,815,354; and Walus, 3,850,871.
It would be highly advantageous if non-migrating polyester plasticizers suitable for use in PVC resins and which exhibit good plasticization efficiency so that they can be utilized at low levels could be produced from low cost and readily available reactants. It would be even more desirable if these plasticizers impart desirable processing characteristics to the PVC resin and exhibited reduced tendency to mar polystyrene and ABS resins. These and other advantages are realized with the improved copolyester plasticizers of the present invention.